Many solid-phase immunoassays involve surface illumination and consequent light emissions from molecules attached to the surface. Generally, these emissions travel in all directions. Either these divergent emissions must be collected with expensive and awkward light collection optics to achieve sensitivity or the inherent inefficiencies and consequent low signal to light level ratios must be accepted.
Diffraction gratings cause light to be diffracted into specific angles as contrasted to being scattered in all directions. The original gratings were prepared by ruling a number of straight, parallel grooves in a surface. Incident light is diffracted by each of the surfaces and is principally directed in directions in which light from each groove interferes constructively with light scattered by the other grooves. This constructive light interference property of a grating allows efficient collection of light. Diffraction gratings have been used for dispersing light into its spectral components.
Many assay systems have been developed using different physically measurable properties of reagents to provide a measurement of an analyte concentration in a sample. Radioimmunoassay (RIA), immunofluorescence, chemiluminescence, enzyme immunoassays (EIA), free radical immunoassays (FRAT), light scattering nephelometry, transistor bridge probes, indium reflective surfaces, and ultrasonic probes have been applied. These systems use the highly selective reaction between a primary binding reagent material such as an antibody or antigen and an analyte selectively binding therewith. Due to limits of sensitivity, however, prior art systems have required the use of relatively large analytes, such as antibodies or large antigens, or require the use of sandwich assay techniques to increase the detectable signal.